The following discussion of the prior art is intended to present the invention in an appropriate technical context and allow its significance to be properly appreciated. Unless clearly indicated to the contrary, however, reference to any prior art in this specification should not be construed as an admission that such art is widely known or forms part of common general knowledge in the field.
Known separation devices of this type typically include a thickening tank and a feedwell disposed generally within the tank to contain feed slurry. The feedwell is comprised of a single chamber having an inlet for receiving feed slurry and at least one restricted outlet for directing the slurry into the thickening tank. The feedwell is configured to reduce the turbulence of the incoming feed stream, to allow reagents to be mixed into the slurry, and to allow for reaction between reagents and the feed material before the treated slurry is discharged into the thickening tank. The configuration of the feedwell also promotes even distribution of slurry flowing from its outlet into the thickening tank.
Known extraction devices do not optimise the mixing and distribution of liquid entering the thickening tank from the feedwell outlet. They suffer from back-mixing of liquid from the thickening tank into the feedwell as well as short-circuiting of liquid flow from the feedwell itself. Another shortcoming, in some circumstances, is that insufficient residence time is provided to allow for optimum reaction of flocculants and reagents. Similarly, the residence time is often insufficient to allow for staged addition of reagents, requiring additional upstream tanks to be added, in turn increasing cost and space requirements.
It is an object of the invention to overcome or ameliorate one or, more of the deficiencies of the prior art, or at least to provide a useful alternative.